The present invention relates to an earth nut for use in fixing a metallic part, of which surfaces are coated with paint, to a mating member such as a vehicle body or the like in grounding condition.
Conventionally, a nut 20 having a toothed washer as shown in FIG. 4 has been used to fix a metallic part, of which surfaces are coated with paint, to a mating member such as a vehicle body or the like while ensuring grounding. The nut 20 with the toothed washer comprises a washer 22 having a multiplicity of pointed teeth 21 formed on a periphery of a metallic plate and a nut body 23 to a lower end of which said washer is attached such as by welding. When the nut 20 with the toothed washer is rotated, tip ends of the teeth 21 cut and peel off a coating film on a seat surface, with which the nut contacts, to get at a metallic portion inside the metallic part, thus providing for electrical conduction.
Even when the teeth 21 get at the metallic portion inside the coating film to ensure electrical conduction between the nut body 23 and the metallic part, however, the metallic part cannot be sometimes grounded to a mating member such as a vehicle body or the like because electrical conduction cannot be provided between the nut body 23 and a bolt in the case where the coating film adheres to screw threads of the bolt, onto which female threads of the nut body 23 are screwed.
Also, there has been caused a problem that, when a high axial force acts on the nut 20 with the toothed washer, the teeth 21 on the washer 22 experience permanent set in fatigue to eliminate electrical conduction between the nut and the metallic part.
Further, there has been caused a problem that, when the coating film adheres to screw threads of the bolt, the coating fills screw valleys when the nut is screwed onto the bolt, resulting in defective fastening.
Besides, there has been caused a problem that the nut with the toothed washer are composed of two pieces including the washer 22 and the nut body 23, which leads to an increased cost.
The present invention has been accomplished to provide an earth nut which is capable of solving the above described problems of the prior art, that is, an earth nut which is capable of surely fixing a metallic part to a mating member such as a vehicle body or the like while grounding the metallic part even if a coating film adheres to screw threads of a bolt, and which is free from the possibility of losing a grounding function even upon application of a high axial force and is low in cost.
The earth nut of the invention having been accomplished to solve the above described problems comprises a flanged nut having a flange, which is formed at a lower end of a nut body to be integral with the nut body, a plurality of projections formed at a lower portion of the flange near an outer peripheral edge of the flange for enabling cutting and peeling off a coating film on a seat surface, with which a bottom surface of the nut contacts, and a plurality of longitudinal grooves provided on screw threads of a female thread portion of the nut body to extend axially of the nut body and having edges on one sides of lines of intersection of the screw threads of the female thread portion of the nut and the longitudinal grooves to peel off a coating film adhered to screw threads of a bolt, onto which the nut are screwed.
In addition, it is preferable that the projections are formed by downwardly pressing upper portions at a plurality of locations near the outer peripheral edge of the flange.
Further, it is preferable that the projections are three in number and are equally distributed
Because the earth nut of the invention comprises the longitudinal grooves (with edges) provided on screw threads of a female thread portion of the nut to extend axially of the nut body, the edges can cut and peel off a possible coating film adhered to screw threads of a bolt to provide electrical conduction between the bolt and the earth nut. Further, failure in fastening of the nut is not generated since the coating peeled off can be discharged outside the nut through the longitudinal grooves.
Also, because a coating film on a seat surface, with which a bottom surface of the earth nut contacts, can be cut and peeled off by the projections formed at the lower portion of the flange near the outer peripheral edge of the flange, it is possible to fix a metallic part to a mating member while effecting grounding.
Further, since these projections are formed by making use of a portion of the flange of the flanged nut, they will not undergo permanent set in fatigue even in the event of being acted by a high axial force, and so the nut can exhibit a loosening resistant effect and attain cost reduction due to the possibility of one-piece design.